Problem: Suppose the area of a circle is ${16\pi}$. What is its circumference?
Answer: ${K = 16\pi}$ ${c = 8\pi}$ First, find the radius: $K = \pi r^2$ , so $r = \sqrt{K / \pi} = \sqrt{{16\pi} / \pi} = {4}$ Now find the circumference: $c = 2\pi r = 2\pi \cdot {4} = {8\pi}$.